Pharaoh Coupling Caps

[bordonbert]

Hi Midwayfair.  I think you may have missed the point of what I was trying to say with my example figures.  I was trying to put a little perspective into the situation with an example of some basic theory.  Unless you know the people who are posting, you can never tell how much they understand of what is going on and it is better that they become aware of a little of what they are doing rather than just plug in values at random.  I always take the line that too much info is better than too little with apologies to the already informed.  With too little data the wrong issues get addressed and the myths begin.

The numbers I used are certainly exaggerating the effect it will have in this case but the theory is correct and it was only the theory I was trying to illustrate.  Multiply the capacitor by a factor of 10 and you drop the cutoff frequency by the same factor.  I'm sure we don't disagree on that.  I chose 400Hz and 40Hz for my example simply because it would be clear to see that it is a serious issue and needs consideration.  It wasn't meant to relate to the real problem that the poster was having.

Without knowing the input impedance of each stage, ('the' reusable stage in effect), we can't guess at the current 3dB point.  It is confused by having to take into account the shunt feedback applied via the 470k resistor which drops the value of that resistor considerably from its 470k.  You have missed the effect of that in your 470k//100k suggestion, it is not just a case of paralleling the two values!  As the feedback resistor has the small input voltage at one end but a much larger voltage on the other output end it appears to the input as though it is a very much smaller resistor than its value, (sort of bootstrapping in reverse)!  Then there is also the paralleled effect of the low non linear impedance of the feedback diodes as they turn on and off which we have ignored.  I would suggest that that input impedance may even be generally below 40k and could even drop lower than 10k under some conditions!  All of this pushes our frequency up way above what you seem to be suggesting.  If it slips down to even 40k, (a definite in this situation I would suggest with an open loop gain before feedback of 100x for each stage), the frequency has become: 1/2*Pi*40k*0.047uF which is 84Hz.  The lower it goes, the higher the frequency goes and we are already conservatively within the range of the guitar.

The point here is that, as you and I have both pointed out, if the cutoff frequency sits down close to or below 82Hz there is nothing to be gained by changing all of the coupling caps to 470nF at all, and lots to be lost!  So I suggested changing the caps one at a time and by values a lot less than 10X and playing by ear as to when to stop.  No change?  Then change back!

And of course, 6dB/octave and 20dB/decade are interchangeable to all intents and purposes, it is just that often one is clearer to envisage than the other depending on the circumstances, and 47nF to 470nF is also 10x.

[Hexjibber]

Not enough balls?  Never heard that complaint before.... 

Just curious how yours compares to this demo here of the King Tut.

PCB and Schematic Link:
http://www.rullywow.com/product/king-tut-fuzz-pharoh-clone-pcb/

I'm only working from memory at this point but my King Tut build doesn't seem to be quite as aggressive as yours sounds in the demo (I'm using a Mex '72 Deluxe Tele and Blackstar Series One 6L6 just as an fyi). It's hard to describe and the difference is only slight but to get close to the sound I want I have to dime the gain on full (silicon diodes) and even then it just sounds a bit polite for a Muff, just not as saturated and snarly and boomy as I was expecting. By comparison my recent Musket build is the sort of over the top fuzz I was hoping the Pharaoh would be, obviously it has the LPB-1 in front for extra hair but even without that on at all it's just a lot more aggressive gain wise and has a bigger low end response.

I'm going to try swapping out all the 47n caps for 470n just to see what it does for my own curiosity but could there be other factors at play like the 2N5089s and MPSA18 I used, is their hFE responsible for any differences here? I seem to remember I just used all the highest ones I had for maximum brootal toanz!

All good fun anyway, I hope this doesn't read as a critique on your board dude cos it definitely isn't, I would probably never have even looked into it had I not by chance read another unrelated post about all the coupling caps being 470n.

Will let you know how I get on!

[bordonbert]

I posted in another thread:-

"A warning.  Different transistors will make no difference to this circuit, (they rarely do), don't fixate on that!

"The circuit uses very basic standard elements to perform each task.  The first two transistor stage has been around since Adam and the final stage is a classic single transistor amplifier.  They both employ local negative feedback, (it's a GOOD thing), within them.  One of the jobs negative feedback is used to do is to make the circuit immune to differences in the gain of the transistors.  For all modern transistor types like the ones you  listed it works.  'Nuff said?"

That applies here also.  It's one of the reasons why designers use negative feedback!  As long as you have modern normal gain transistor types in working order their hFE will make no difference at all to this circuit.

Apologies if I give you loads of tech info and explanations you don't want but there are others out there who would be interested to understand what is going on, not just get their pedal moving.  This one will work but what about the next and the one after that?  Almost inevitably nowadays, info based on good sound engineering fact often spoils what we want to think is the case or points to a solution we don't want to follow.  Mostly people are going to do what they are going to do anyway and are really only looking to be told that is the best option.

Anyway, I'm sorry, no more long descriptions from me.

[Hexjibber]

I posted in another thread:-

"A warning.  Different transistors will make no difference to this circuit, (they rarely do), don't fixate on that!

"The circuit uses very basic standard elements to perform each task.  The first two transistor stage has been around since Adam and the final stage is a classic single transistor amplifier.  They both employ local negative feedback, (it's a GOOD thing), within them.  One of the jobs negative feedback is used to do is to make the circuit immune to differences in the gain of the transistors.  For all modern transistor types like the ones you  listed it works.  'Nuff said?"

That applies here also.  It's one of the reasons why designers use negative feedback!  As long as you have modern normal gain transistor types in working order their hFE will make no difference at all to this circuit.

Apologies if I give you loads of tech info and explanations you don't want but there are others out there who would be interested to understand what is going on, not just get their pedal moving.  This one will work but what about the next and the one after that?  Almost inevitably nowadays, info based on good sound engineering fact often spoils what we want to think is the case or points to a solution we don't want to follow.  Mostly people are going to do what they are going to do anyway and are really only looking to be told that is the best option.

Anyway, I'm sorry, no more long descriptions from me.

I appreciate the comprehensive response man, no need to apologise! While that side of pedal building currently falls outside my level of understanding I am always keen to expand that knowledge!

I'd read as much to know that transistor hFE does not affect the Muff circuit significantly, I suppose I was just musing on other reasons that my build isn't quite hitting the mark.

I've got it into my head now that these caps are going to make all the difference, we'll see I suppose!

[selfdestroyer]

I posted in another thread:-

"A warning.  Different transistors will make no difference to this circuit, (they rarely do), don't fixate on that!

"The circuit uses very basic standard elements to perform each task.  The first two transistor stage has been around since Adam and the final stage is a classic single transistor amplifier.  They both employ local negative feedback, (it's a GOOD thing), within them.  One of the jobs negative feedback is used to do is to make the circuit immune to differences in the gain of the transistors.  For all modern transistor types like the ones you  listed it works.  'Nuff said?"

That applies here also.  It's one of the reasons why designers use negative feedback!  As long as you have modern normal gain transistor types in working order their hFE will make no difference at all to this circuit.

Apologies if I give you loads of tech info and explanations you don't want but there are others out there who would be interested to understand what is going on, not just get their pedal moving.  This one will work but what about the next and the one after that?  Almost inevitably nowadays, info based on good sound engineering fact often spoils what we want to think is the case or points to a solution we don't want to follow.  Mostly people are going to do what they are going to do anyway and are really only looking to be told that is the best option.

Anyway, I'm sorry, no more long descriptions from me.

I appreciate the comprehensive response man, no need to apologise! While that side of pedal building currently falls outside my level of understanding I am always keen to expand that knowledge!

I'd read as much to know that transistor hFE does not affect the Muff circuit significantly, I suppose I was just musing on other reasons that my build isn't quite hitting the mark.

I've got it into my head now that these caps are going to make all the difference, we'll see I suppose!

I can agree with you also. Mine is not as aggressive sounding as Rullys demo. I have tried it with my SG with burstbuckers and my strat with single coils. I need to open mine up and see what transistors I ended up using since I may have used some NOS ones I had laying around and not the MPSA18 & the 5089's. I will check tonight.

Cody

[bordonbert]

One last attempt.  There are versions of this circuit out there using MPSA12, MPSA18, 2SC1815, 2N5089 and doubtless more transistors.  All of these versions work, possibly to different tastes but consider the following:

MPSA12 - min hFE 20,000  (it's a darlington and effectively 2 transistors connected)
MPSA18 - min hFE 500
2SC1815 - min hFE 70
2N5089 - min hFE 400

that's a range of 70 - 20,000.  In the light of that, do you think it matters?

(I'm suffering from Cassandra Syndrome.)

[luks999]

since im building this thing too soon (pcb ordered) one question:
where did you read exactly of the different cap values?

this one i found looks exactly like the schematic of the rullyvow document
http://www.bigmuffpage.com/images/schematics/Pharaoh%20Big%20Muff%20Clone%20Schematic.jpg

[Hexjibber]

since im building this thing too soon (pcb ordered) one question:
where did you read exactly of the different cap values?

this one i found looks exactly like the schematic of the rullyvow document
http://www.bigmuffpage.com/images/schematics/Pharaoh%20Big%20Muff%20Clone%20Schematic.jpg

If you read the Pharaoh thread on FSB there is a schematic showing 470n and also a vero layout.

Plus in that photo I posted earlier in this thread of a Pharaoh board you can see the larger caps.

[Hexjibber]

Here's another, they don't look like 47n to me..

[luks999]

here i found the layout
http://tagboardeffects.blogspot.co.at/2012/02/black-arts-toneworks-pharaoh.html
youre right, all 470n instead of 47n. strange. the rest seems the same to the king tut

hmm yes i know you may be right, but its hard to say. there may be also big 47n caps.

now im confused what i should use :/ guess im stucking with the 47n (read in this thread there may be a bass cutoff when using bigger caps)

[luks999]

seems youre right they seem to be all 470nF
here i found a thread for this:
http://www.madbeanpedals.com/forum/index.php?topic=10249.10

--> interesting thing here is the fifth pot its the attack. i think i will try that one too (if theres space haha)

some veros with this values are verified and to me, the pic also speaks for that (bigger caps)
http://www.sabrotone.com/?attachment_id=2373

i think i will use 470n too
does anyone compared how the 470 sound to the 47n caps?

[pierre67]

hi !
I have 2 King Tut builded, one with 47nF and the other one with 470nF. What I can tell is the first one (rullywowr's version) sound pretty good, lows are tight and maybe a little less agresive than the 470n version...this one (.47µF) sounds similar to the demos you find in youtube, more agresive, and with a lot more bass...in general very "brut"...I can't make a sound sample (and even if I could I wouldn't do it, because my guitar playing sucks more than my english ), but in the end, which one tends to sounds more like the original? I guess the .47µF version. Which one I prefer?...for my taste, the rullywowr's one, without the no clipping option (too loud for me).

[bordonbert]

now im confused what i should use :/ guess im stucking with the 47n (read in this thread there may be a bass cutoff when using bigger caps)

No Luks, it's the opposite.  You really need to go back and read the posts again a little slower.  The issue is: "higher value caps will lower the cutoff point and give us more bass but does it need that doing in the first place?  You could say "let's just do it anyway, even if it doesn't make any difference to the sound it won't matter will it?" but that's not true.  You don't want to take the cutoff points lower at the bottom or higher at the top end further than they need to be because it doesn't alter your sound, it just opens the door to muck you don't want.  50Hz is less than an octave below a guitar bottom string and 60Hz is even closer!  Do you want to increase the amount of hum and low frequency noise?  Do you want slight power supply pops to become big thumps?  That's clearly spelled out in a number of posts in this thread.

If you have a bigger value or even values available try the following.  Change a single cap to 100nF, that's dropping the cutoff point of one filter by a whole octave.  If it doesn't change what does that mean?  Does it mean you haven't made it big enough?  Does it mean they must all need changing?  No!  If they are well below the value they should be and therefore need increasing there will be a change with the first replacement.  So it makes sense to continue to see if there is more to be gained, if it doesn't have any effect there will be no point in going any further so change it back.

If that improves things a little change the second to 100nF.  If it does increase the first to 220nF.  (I'm doubling the value each time to give you a whole octave of improvement.  You will hear any genuine improvement over that range.)  See if that improves things more.  And so on.  Stop when there is no further improvement.  That way you will get the best sound you want in the shortest time and introduce no more problems than you need to.

Guessing whether it's alive and poking it with a stick to see if it moves is not going to give you the best results you can get and I'm sure that is what you would want.  This doesn't take experience and knowledge, it just takes a little patience and the ability to ignore your signature when you will really benefit from it.

(I take it you don't agree with Newton and his "If I have seen further it is by standing on the shoulders of Giants" comment?)

[luks999]

hey dudes

sorry i got that wrong, sure the earlier posts say 470n = more bass.

@pierre: Thanks. It sounds i will like the 47n more, because i dont want the fuzz be too bassy, brutal and muffled
too bad you cant make a demo. and dont worry about your playin not everyone here is a guitar pro (i play pretty bad too)

@bordonbert: thanks for the detailled info here thats a good idea. so i guess the easiest way would be socketing these caps and try.

another idea that i had: if there is a 5 way toggle switch (found a 4pdt on musikding, but necessary would be a 5pdt), then it would be possible to include a switch to change the fuzz from the rullywow values to the original values. or is that too much effort?
just an idea (but yeah the fuzz has a lot of switches already)

[pierre67]

I think it would be easier to socket those caps, or build two King Tut...it's not an expensive project after all...or try fist in a vero layout and see wich one you like more.

Regards from Brussels, city of riots.